Physics 101
Classical Physics
Spring 2010
Homework 10 Solutions
DUE IN CLASS ON April 15
1. If the frequency of a wave is 200 Hz, and the wavelength is 2 m, how much time
is required for a single wave to pass by an observer?
(a) 0.005 s
, (b) 0.050 s, (c) 200 s, (d) 400 s, (e) 800 s
Since the frequency is the number of wavelengths that pass a given point per unit time, the
time for a single wave to pass an observer is 1
/f
= 0
.
005 s.
2. If the frequency of a wave is 200 Hz, and the wavelength is 2 m, what is the
velocity of the wave?
(a) 0.05 m/s, (b) 0.50 m/s, (c) 200 m/s,
(d) 400 m/s
, (e) 800 m/s
The velocity is given by the product of the frequency and wavelength
v
=
fλ
= 400 m/s.
3. If the frequency of a wave is 200 Hz, and the velocity is 10 m/s, what is the
wavelength?
(a) 0.05 m
, (b) 0.50 m, (c) 200 m, (d) 400 m, (e) 800 m
Solving the relation used in problem 2 for the wavelength,
λ
=
v/f
= 0
.
05 m.
4. A transverse wave travels along a perfectly elastic string parallel to the ground.
Any given point on the string:
(a) doesn’t move
(b) moves up and down
(c) moves up only
(d) moves left and right
(e) depends on how high off the ground the string is.
5. A standing wave:
(a) can be constructed from two similar waves traveling in opposite directions
(b) must be transverse
(c) must be longitudinal
(d) has motionless points that are closer than half a wavelength
(e) has a wave velocity that differs by a factor of two from what it would be for
a traveling wave
For example, the superposition of 2 waves travelling in opposite direction with the same
frequency and amplitude can be written as
A
cos(
kx

ωt
) +
A
cos(
kx
+
ωt
) = 2
A
cos(
kx
) cos(
ωt
)
Then a given point at
x
executes simple harmonic motion, which gives a standing wave.
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 Spring '09
 Physics, Work, Wavelength, 6 m, 1m, 2 2m, 6 W

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